Esterification oe cellulose



May-1, ma. 1,668,484

H. L. BARTHELEMY ESTERIFICATION 0F CELLULOSB Filed Jan. 27. 1928 s sheets-shew. 1

TemPeratm-e TToRac z H. l.. BARTHLEMY ESTERIFICATION AOF CELLULOSE Filed Jan. 2'?, 1928 5 Sheets-Shes. 2

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May l, 1928. 1,668,484

H. L. BARTHLEMY ESTERIFICATION oF cELLULosx;

Filed Jan. 27. 1928 3 Sheets-Sheet 3 Patented May 1, 1928.

UNITED STATES "PATENT OFFICE.

HENBILOUIS BARTHVLEMY, OF VERCELLI, ITALY, ASSIGNOR TO RUTH ALDO COM- PANY INC., 0F NEW YORK, N. Y., A CORYORATION 0F NEW YORK.

ESTERIFICATION OF CELLULOSE.

Application led Januaryi27, 1928, Serial No.` 249,988, and in France December 29, 1927.

The object of the present invention is a new process oi manufacturing cellulose esters, particularly acetyl-celluloses. The. raw material may consist of wood cellulose or `of cotton which may (or not) have been trans' formed beforehand by a special process such (a) An oxidation process according to the known practice, or preferably according to the United States patent application No.

209,167 filed on the 28th July, 1927, for an 4 (c) A process of preliminary and partial esterification by a min-eral or organic acid,

such `as nitric acid or formic acid; p

((Z) A process of preliminary and partial. etherification by an alcohol, such as benzyl alcohol or ethyl alcohol.

Up to the present, the csterification of cellulose-previously subjected, or not, to one of these preliminary treatments-has been etl'ected by the action of acetic anhydride and of a catalyzer such as sulphuric acid, in the presence of a diluent usually consisting of acetic acid. The various processes employed may be classed as follows:

l'. The cellulose is introduced into the whole of the acetylating bath, consisting of a mixture of the anhydride, acetic. acid and catalyzer, with or without a solvent such as benzol.

This method of procedure is disclosed in the French Patents No. 368,738 of th June, 1906; No. 458,263 of 22nd May,v 1913; No. 449,253 of 28th August, 1912; No. 523,738 of 9th October, 1920; and 505,608 of 31st October, 1909and in the German Patents No. 184,201 of2nd October, 1904; No. 25.,- 706 of th September, 1905; and No. 269,- 193 of 28th December, 1909.

Il. The cellulose is steeped in acetic Vacid and is then immersed intothe whole of the anhydfifhlc and catalyzer, with or` Without the presence of a. solventsuch imitant.-

` is added afterwards.

This is the process of the United States Pat.w ent No. 1,236,578 of 14th August, 1917.

III. rlhe cellulose is hydrolyzed in the whole ofthe acetic acid and catalyzer, the whole of the anhydride being then added, with or without the addition of a solvent such as bezol. This method of operating is 1n accordance with the United States Patents, No. 1,236,579 of 14th August, 1917 and 845,374 of 26th February, 1907; the French Patents No. 319,948 of 22nd March, 1902. 458,079 of 27th September, 1905 and 565,- 654 of 30th April, 1923; and the German Patent No. 163,316 of 9th October, 1905.

IV. The cellulose is hydrolyzed beforehand in the whole of the acetic acid and the catalyzer, in the presence cfa small amount of acetic anhydride. The acetic anhydride This method is in accordance With the French Patents No. 473,- 399 of 12th June, 1914 and No. 478,436 of 4th August, 1914.

V. The cellulose is entered into the Whole of the acid, with addition of the acetic anhydride. kThe catalyzer is then added, all at once or -in several portions, as in the fol lowing patents: French Patent No. 494,832 of 24th May, 1917, Vand Swiss Patent No. 120,810 of 28th September, 1925.

VI. rThe cellulose is subjected to a continuous series of partial esterifications, all of which. are characterized by a. series of successivel additions of suitable quantities of the acetylating agent, such additions being deferred untilthc state of equilibrium corresponding to the fresh addition which has brought about the change of concentration has been established. The catalyzer is added at the same time as the first portion. of the acetic anhydride. y cation insistence is laid on the fact that the manner in which the, various acetylation agents are caused to act on the cellulose is not without its efl'ect on the intrinsic value of the final product.

The fact is that esterification of cellulose or its derivatives is not at once a system of reaction` rin homogeneous equilibrium, the monoand cli-acetates formed at first being, indeed, insoluble in the acetylating medium. Moreover, seeing that the acetylation is a very highly exothermic reaction, the homogeneity of the final product depends, for the nest part, on the skill which the acetylation. is performed, that the' skill In this patent applig With Which'local rises in tcmpeature are prevented. These rises occur all the more readily at the commencement of the esteriiicationzbeeau'se ithe cotton-:remains abadi-icon- 5 ductor olgheat until ithas become thoroughly soaked.

vApplicant has ascertained-'wand this is 4the subject of the present invention-that the reaction can -be very easily Ucontrolled,l and i `at the same time cellulose acetates Whichare completely homogeneous in respect oi: optical, mechanicaland plastic properties can be obtained, by employing the new andV original working method hereinafterdescribed.V

i VVThis Working method consists 'in adding .to Athe cellulose :a succession oil complete acetylation baths (that is to saybaths lcontaining'the catalyraer, the acetic anhydride f andthe-diluent, such vas acetic acid) .in such "ma "manner that the'heat of 'theyrcactionv 1s 4readily dissipated, mainly during vthe .,iormation of fthe cellulose monoand "diacetates, this being doneivithout 'the necessity 5f-resorting to a preliminary hydrolysis.

a5 The operation is considerably facilitated. by

"thetact that the cotton isso'ftened prior t'o'i-- acetylation (inthe .manner specified in "theUnited 'States ,patent` apljlieation` tiled .lthis d ay, inthe name of the. applicant, for

12:0` .a Process for., softening fibres .of cellulose origin with a vvievv tofacilitating their esteritication.)

'"In bringing about a succession ot conditions of Vchemical equilibrium v.Which, :While "35."di'l'lering 'slightly lirom one another, vare -nevertheless 'suiiiciently ren'ioved l'or the rises #in temperature. not to exceed' 5 or GQC., so long as "the amount o'lilfthe acetyl radi'cles combinedhaswnot reached the heat oi'v 4o the reaction is perfectly subdivided and .ab-

r yunits liberated by .the esteritic'ation, said heat units being determined bythe composi- .tion of the various acetylating baths.

Eachpstateot equilibrium of the system Vis regulated, 1n perfectqha'rmony `withl each bath'by ltheA Giilberg and dei'/Vaage law.

According to 'the invention, the catalyzer yemployedis sulphuric acid, Aeither alone' or in association With agents, such as the halogens, which modify cellulose,or again y 'Withoxidizing agents as prescribed .in'fthe hibitr a' notable dll UnitedStates patent application No. 209,166 tiled 28th July, 1927, for a Process for the manufacture of cellulose esters. In the :composition of the different baths the amount of sulphuric acid employed is progressively increased; and that, too, at the commencement oit the esterilication; because applicant has recognized that the fact of esterifyingthe. celluloseprogressively enables it to `stand progressively increasing amounts ol the cat-alyzer. the operation isjcoiuluctcd with very small lamounts ot' sulphuric acid, associated preit' erably -with halogens. This association should preferably occur "in fthe tirst :stages -ot esterilication, -rbefore theuicetyl content exceedsabout 10%. The fact of the halogens heing'employed indirect association enables a considerable reduction toy be eected in the quantity ot' the sulphuriciacidfiwhich, as :is

known, causes the formation of cellulosesul- "phates, ithe stability-fof which Vis fmediocre,

and which make the acetates diliicult to store.

Although thefcatalyticV action ofthe halogens islnowin'it hasnever yet been utilized in this mannen in adm-ixture With sulphuric acid lin the lirst 4phase/of-theoperation. .The

`method of employing chlorine:described .fin `the French Patent No. 505,60Sot Slstflctober, 19l9, for example, places thexoperatorw' `under 'theineces'ity of artificially raising the reaction mass to elevated temperatures, at-

taining Z0-80O C., lwhich may :have serious consequences. On 'the other hand, .the association `of fthe catalyzers enables the opera- ,tion to he conducted with temperatures ot 1092505 C. -iforthe heat of rcactioll.

iln Athe process forming Ythe subject oli-the present in vention,the range o'l temperaturcs is 'clearly restricted, theexpcrinlents oli the applicant havingdemonstrated that the `rate ot fixation voili the acetyl radicles'on the celmust only beincreased Very gradually,fai ling Which the products obtained may differ totally in character. A whole-series of experiments have convincedtheapplicant that twoipartially acetylated*celluloses will vexierenice` in-'stherate and intensity of acetylation during `their "successive periods ot'cstoritication it" they were At the outset,

lli!) ilulose complex already partially Aacetylatcd Y not, at the outset, in the saine condi-tionlof richness -in acetylgroups andV were not at the sametemperature. 'lhe accuracy ot'tlus `observation persists even when the said :par-

tialuinitial acetylation has beenfreliected in the same bath and at the saine ten'iperature.

In the process according to this invention,

thetemperature ofthe reaction is limited to `between 18 and 26 'during the preparation o'l the cellulose-acetates with an acetyl `conitentbetweeirO and 11.70%` (monoacetate in C l2). In the preparation ot the dif, triand 1up to the tetracetate of cellulose, the tempervature is preferablymaintained between :20

and Finally, in order ultimately to obtain the pentaand hexacetates of cellulose Without being obliged to employ too great an excess of acetic anhydride, the temperature may be allowed to rise, without inconvenience, to -650 C. This elevation of the temperature is then no longer attended with any danger to the cellulose complex, which is already in an advanced and uniform stage of acetylation which protects it vfrom the rough action of the catalyzers.

These diiierent results are obtained by a series of additions, in so to speak elementary quantities. -The con'iposition of these additions, and theamount and number oi each, are calculated as herein set forth. There is nothing similar existing in the literature. The British Patent No. 190,732 of 20th June, 1921, comprises only two phases of acetylation, whereas applicants process, on the contrary, comprises a minimum of four phases, as will be shown in the subsequent example; but, in practice, their number may be far greater. Moreover, Whereas the first phase of the process described in the British Patent No. 190,782 is' carried through without any condensing agent, and at temperatures which may attain 90-1000, the `tirst phases of the present process are carried out in presence, conjointly, of sulphuric acid and an auxiliary catalyzer such as a halogen-chlorine, bromine or iodine. The range of temperature lies between 18 and 26 C.

The present process also differs from the process of the previously mentioned French Patent No, 473,399 ot 12th June, 1914i, in that the said' latter process also comprises only two distinct phases. Furthermore, the condensing agent is added solely in the iirst phase and consists only of sulphuric acid, or of methylene sulphate, as l'in the French Patent No. 478,436 ot 4th August, 1914, its chief purpose being to effect the hydrolysis of the cellulose, as specified in the resume. The next bath is composed solely of acetic anhydride; whereas in the process now described each of the baths is complete, that is to say, contains acetic anhydride, the cata.- lyzer and a larger or smaller amount of acetic acid, serving as diluent in preference to benzol and carbon tetrachloride, which lead to the `formation olf acetylcelluloses with a morphological structure v identical with.

y cotton.

and the ordinates represent the temperatures.

This will show the manner in which the various successive acetylations are conducted, and how the amounts of heat disengaged in the course ot the reaction are balanced with a view to contributing to the final result, which is a cellulose acetatehaving the maximum of optical, mechanical and plastic homogeneity.

The relative proportions of the various reagents are summarized in the graphs Fig. 3 and Fig. 4, respectively relating to Example I and Example Il. These graphs represent the relative amounts of anhydride, acetic acid and sulphuric acid ot which each bath is composed, at the times at which the additions are made. The abscissas denote the times corresponding to the graph ot the recording apparatus, and the ordinates the amounts of acid or anhydride, expressed in litres, and the sulphuric acid in cubic centimetres.

70 kilograms of dry, boiled cotton are treated by the primitive softening process referred to at the beginning, said process consisting in vaporizing throughout the mass 70 kg. of 99% acetic acid supplied by an auxiliary boiler. The temperature is allowed to return to 16.5O C., and at that moment-that is to say at 9.15 of the graph No. 1 of the recording apparatus-the succeeding bath is poured on to the cotton, which is maintained in agitation in an apparatus of the Ve'rner mixer type, the Grignard type, or preferably in an apparatus of the type described in the applicants United State patent application No. 209,164 tiled on 28th July, 1927 for Improvement in apparatus for the acetylation of cellulose.7 The bath has the following composition:-

(a) Glacial acetic acid...,. litres. Acetic anhydride (93%), 17 litres. Brornine 0.020 kilograms. Sulphuric acid (95.5%)" 0,070 litres.

`lrornine -i 0. 018 ki Sulphuric acid (95.5%) 0.090 litres,

This new acetylation is characterized by a fresh rise in temperature, and by the production of a more highly acetylated acetate than the previous one, the acetyl value being Fig. 1).

1.47% after equilibrium has been restored.

At 12.00, the next bath is added, which doesj not contain any halogen, and has the composition (c) Acetic-acid (crystallizablc) 57 litres. Acetic anhydride (93%) 4 litres. Sulphuric acid (95.5%) 0. L100 litros.

The temperature again rises, but not above 230. When ecpiilibrium is once more restored by the masses present, the acetyl value is 7% and at the same time a uniform modification of the optical properties of the libre, when viewed by polarized light, begins to be manifest.

Al'. 113.30- thefollowing fourth bath .is added, containing a larger `amount ofV sulphuric` acid p (d) Glacial acetic acid v 55 litres. Acetlc anhydride (USL/L 6 litres. Snlphuric acid (95.5%)- 0.000 litres.

(e) Glacial acetic acid- 7 litres. Acetc anhydride (93%) ,1.413 litres. Sulphuric acid (95.5%)-- 0. 050 litres.

At this moment the reaction isv preferably conducted in tWo stages. At first the temperature is allowed to rise' spontaneously during -40 minutes, Without external cooling, so that the reaction mass has the temperature 2.528O C., whereby the reaction is restricted to the production of a cellulose acetate with 25-28% of acetyl. This acid swells up considerably and uniformly in the re-agents and is ready to enter into solution. I

At 19.00 thev reaction is terminated by the applicationv of external1 heatso as to raise the temperature to 604550 (exactly 620 in At 20.00 a remarkably limpid and refractive acetic collodion is obtained, a sample of which, on precipitation in Water, Washing and drying, shows 45.3% of acetyl, corresponding approximately to the hexacetylcellulose in C 12.

The acetic sol can be precipitated in water, after filtration. It may bei treated in situ, or in any other suitable apparatus, by the known methods of saponification, such as thosev described in the United States Patent No. 838,850 of 23rd November, 1904i, or preferably' by the process specified by the present applicant in hisUnited States patentappli'cation No. 209,162 filed 28th July,

On equilibrium beeV 1927, for a Process of manufacturing cellulose esters.7

)rampa` 11.

Brmnine (dissolved and uncomhinrd) litres.

o. 05e kilograms. the object of this bathbeing to further increase the softening (cuticular and protoplasmic) of the cellulose. v t At 9.00 of the graph (Fig. 2), the following bath is introduced, by suitable pouring means, the cotton being kept in agitation by mechanical means (b) Glacial acetic acid litres. Acetic anhydride (93%)- 18 litres. Bromine 0.018 kilograms. Sulplxuric acid (95.5%) 0.070 litres.

As in Example I, this acetylation ischaracterized by a rise; in temperature froml to 21O C., and by an acetate which, after chemical equilibrium has been established, shows 1.02% of acetyl.`

At 10.00, the second acetylation` bath is added, composed of f (c) Glacial acclziciacid 67' litres.

Acci'ic anhydride (93%).. l18 litres. Chlorine, dissolved in the acid 0. 050 kilograms. Sulphuric acid (93%) 0.095 litres.r Y This bath produces a further parti'alacef tylation, characterized, after equi lbrium has been restored, by 2.77% of acetyl.

At 11.30,` the` third acetylation bath is introduced, composed of (d) Glacial acetic acid 58 litres.

Acetic anhydride (93%) 5 litres. Sulpliuric acid (93%) es c. 400 im This bath produces a fresh acetylation, more characteristic in respect of elevation of temperature, which rises from 19'to 22.5 ink ay quarter of an hour. After equilibrium is restored, Vthe'acetyl content is foundftobe At 12.30, the fourth acetylationbath is added, having thefollowing composition (e) Glacial amic acid '54 Miras. Acetic anhydride (93%) S, litres. Sulphuric acid` (95%) 0(50vlitres.

As before, despite the increasedamount of catalyzer, the reaction is far less'energetic,

the temperature only rising from 19 toA 20 Y C. At 15.30, after equilibrium has been restored, the new acetate is characterized by a,

content of 19.3% of acetyl. In polarized light it displays dark alternations like points of stricture in preparation.

It will be easily understood that the acetylation can be carried on by further stages in like manner; but the desirability, existing at the commencen'ient oiE the operation, for such subdivision has become less because the cellulose acetate is now on the point of passing into solution under a slightly' more extended acetylation. The essential point is to have attained homogeneity in the lirstfacetates, to ensure the homogeneity of the final products.

At 16.00, the following, fifth acetylation bath is added to the mass (f) Crystalllzable acetic acid n 1 litre.

Acetic anhydride (93%) 14 litres. Sulphuric acid (95%) u 0.005 litres.

The temperature is allowed to rise spon taneously to 30, which takes about 30 ininutes, by dispensing with all external cool ing. This fifth acetylation is characterized by the formation of a thick pulp of `ibres, with the acetyl value 30.26%. Y

At 16.30, the following sixth and last bath is added (g)Glac1a1 acetic acid 5 litres. l Acetic `anhydride. (93%) 120 litres. Sulphuric acid (95%) 0. O50 litres.

and the apparatus is heated so to raise the temperature to 60435O (G40 in graph 2). At 17.30 a thick acetic syrup is obtained, which is treated in the manner indicated in the previous example.

I claim 1. A process for the esterilioation of cellulose or its transformation products, consisting in subjecting the cellulose mass to a series of at least four successive partial acetylations each of which is deferred until the preceding one has terminated.

2. A process for the esterilication of cellulose or its transformation products, consisting in subjecting the cellulose mass to the action of a halogen, and then to a series of successive partial acetylations.

3. A process for the homogeneous esterication of cellulose, consisting in effecting acetylation in a plurality of stages and in using for-the first stages a mixed catalyzer composed of sulphurc acid in association with at least one halogen element.v

4. A process for the homogeneous esteritication of cellulose, consisting in effecting acetylation in a plurality of stages and in using for the first stages a mixed eatalyzer composed of sulphuric acid in association wi-th oxidizing agents.

5. A process for the esterification of eellulose or its transformation products, coni sisting in subjecting the cellulose mass to a series of at least four successive partial ace tylation steps each of which is deferred until the preceding one has terminated and preventing increases of temperature exceeding 60 C. during at least the first two steps.

6. A process for the esterilication of cellu* lose or its transformation products, consisting in subjecting the cellulose mass to the action of a halogen, and then to a series oil, successive partial acetylations, while pre venting increases ol? temperature exceeding GO C. during at least the l'irst two partial acetylations.

7. A process :for the esterification of cellen lose or its transiforination products, consisting in subjecting the cellulose mass to a series of successive partial acetylations each K of' which is deferred until the preceding one has terminated. and regulating the tempel ture of each partial acetylation in accordance with the desired extent of acetylation to be attained in such step.

8. A process for the esterification of celluH lose or its transformation products, consisting in subjecting' the cellulose mass to a series of successive partial acetylations each of which is deferred until the precedinfone has terminated, and each of which eiljected at a temperature depending on the extent of the acetylation desired to be attained during such step.

9. A process for the esterilieation of cellulose or its transformation products, consists ing in subjecting the cellulose mass to the softening action ot acetic acid; and then to a succession of acetylation baths, each performing part of the acetlyation of the cellulose.

10. A" process for the csteritication of: cellulose or its transformation products, ^onsisting in subjecting the cellulose mass to the softening action of acetic acid; and then adding a succession of acetylation baths each producing a part ot the acetylation oit' the cellulose and each containing sulphuric acid containing a catalyzer.

11. A process for the esterification of cellulose or its transformation products, consist-ing in subjecting the cellulose mass to the softening action of acetic acid; and then adding a succession of acetylation baths each producing a part of the acetylation of the cellulose, and each containing sulphuric acid as catalyzer.

12. A process for the esterilication of cellulose or its transformation products, consisting in subjecting the cellulose mass to the softening action of acetic acid; and then to a succession of acetylation baths, each producing a part of the acetylation of the cellulose and containing progressively increasing amounts of sulphuric acid containing a catalyzer. i

13. A process for the esterification of cellulose or its transformation products, con sisting in subjecting the cellular mass to the softening action of acetic acid; and then to a succession of acetylation baths, each producamounts of sulphuric acid as catalyzer, and

associating With the sulphuric acid in at Vleast some of the baths a halogen.

15. A 'process for the homogeneous esterilication of cellulose, consisting in effecting acetylation in :a plurality of stages andvin using for `the 4first stages a mined 'eatalyzer Containing sulphuric :acid and at least one halogen element.

L16. A process for vtheesteriiication of cellulose or Aits transformation products, consistilng` in -sul'Jjectingthe cellulose mass to a series of successive partial .acetylation steps, each of'ivhich iis deferred until the :preced-4 ing one `has terminated, :and preventing increase of `temperature :above approxi-mately 260 C. .during all steps preceding the last one.

17. A process for the esteriflcation of eellulose or its transformation products, con sisting in 'subjecting the cellulose mass to a series of successive partial acetylationsteps, each of which is Adeferred until the preceding one has terminated and preventing` 'variations of temperature .exceeding Gf C. and also increase oftemperature above approximately 2Go C. during all steps preceding the last. p

18. A process for the esterication of cellulose or its transformation products, lconsisting in subjecting the cellulose mass Ito the f action'of a halogen; and then to a series of successive partial acetylations; andpreventing,` increase of temperature :above :approxin'ia'tely 26o C. during all steps preceding the last one.

.19. A process for the esteriication fof oellulose or lits `transformationproducts, rconsisting in subjecting the cellulose ymass to the action of a halogen.; and then to -a Series of successive lpartial acetylation steps; and preventingl variation `of temperature exceeding GO C. and also increase of temper ture above approximately 260 C. during .all steps preceding vthe last.

'20. A process for the -esteritication ofcellulose or its transformationproducts, consis-ting in subjecting the cellulose mass .to the softening action of acetic acid and a l'ialogen; and then to a succession .of acetylation baths yeach producing Aa Apart of the acetylation of the cellulose; and x preventing increase of temperature v:above `approximately :260 C. during all bathsvpreceding the last one.

2l. A ,process for the esterication of cellulose or its transformation produots, Aconsisting in subjecting the cellulose mass to the softening;` action of acetic acid and a halogen, and then to a succession of acetylation baths leach producing a i 'art of the acetylation of the cellulose, an preventing variation of temperature exceed-in 6o` C. and also increase of temperature a ove approximately 260 VC. during all baths precedingI the last n 22. A process for the esteriiieation of cellulose or its transformation products, by a series of more than two successive artial acetylations effected by a successive dition of corresponding ypartial quantities of acetylation agents. w v

In :testimony whereof I aix my signature.

HENRI Louis BARTHELEMY. 

